Recently, the number of devices connected to internet is increased and various forms of receivers are manufactured. Especially, recent mobile devices have various codecs and resolutions and are basically equipped with network interfaces for connecting to an internet network. In general, mobile devices perform voice communication and data communication by accessing the networks of specific service providers and additionally transmit and receive content at high speed by accessing a network having a broad bandwidth such as Wi-Fi. A conventional broadcasting receiver such as a TV is only connected to a broadcasting network but a recent broadcasting receiver is equipped with a an Ethernet network interface and thus receives enhanced service by accessing an internet network through the Ethernet network interface.
Users want to use services and contents enjoyed in the PC environment through mobile devices while moving and also want to view contents played in a PC on a TV with large-sized screen. Therefore, recent broadcasting receivers provide a supplementary network interface besides an existing network.
Such demands have highlighted the need for new transmission technology. The new transmission technology is a method for effective transmission through an internet network according to a situation of a receiver network. The development of technology for satisfying such demands is started by Moving Picture Experts Group (MPEG) and then the standard called MPEG-Dynamic Adaptive Streaming over HyperText Transfer Protocol (HTTP) (DASH) is established.
MPEG-DASH is created based on HTTP that transmits web services accounting for most network traffic on internet. Since a Content Delivery Network (CDN), that is, an existing network, uses HTTP delivery service greatly, an MPEG-DASH service may be easily applied. Additionally, since it is necessary for a broadcasting receiver to receive and play an image in the level that a user feels comfortable even in a network that does not guarantee Quality of Service (QoS), MPEG-DASH includes rules for a stream configuring an image or an encoding method.
A media receiver may measure a bandwidth at the reception side by measuring the size and transmission time of a currently received content by itself. If the bandwidth at the reception side is reduced suddenly, since content transmission is not smooth, a broadcasting receiver plays content until a media segment in a playback buffer is exhausted and then, if the playback buffer is empty during playback, the broadcasting receiver becomes not capable of playing the content. Therefore, a screen freezes.
The playback time of a media segment may vary according to its size or its encoding method even if the media segment has the same size. For example, if content is encoded in 150 kbps, a media receiver may play the content of 150 kbytes for 1 sec. In order to play the media content seamlessly, the media receiver may need to receive at least 150 kbytes for each 1 sec. At this point, 150 kbps is called a bitrate. Of course, the media receiver has a playback buffer and thus may deal with a temporary drop in bandwidth but may not deal with a continuous drop in bandwidth. That is, while the media receiver plays the content continuously, if media content is received in less than 150 kbytes for each 1 sec due to the bandwidth drop at the reception side, the playback buffer of the media receiver becomes empty and thus may not play the content.
Even if the media receiver has a limited playback buffer in a network environment that does not guarantee QoS, in order to play the media content seamlessly by receiving media streaming, a media server according to MPEG-DASH encodes the media content in consideration of a plurality of bandwidth situation as preparing the media content. That is, the media server encodes one media content in a plurality of bitrates. Additionally, the media server divides the encoded media content by the amount that is transmittable at one time
FIG. 1 is a block diagram of a typical DASH delivery system.
As shown in FIG. 1, the DASH delivery system includes a DASH client device 10, a DASH media presentation preparation server 60, an MPD delivery function server 70, and a DASH segment delivery function server 80.
The DASH client device 10 understands a DASH protocol and may thus receive and play media content according to the DASH protocol. The DASH client device 10 monitors a network bandwidth at the current reception side and receives media content according to a current bandwidth.
The DASH media presentation preparation server 60 performs DASH media presentation preparation. For this, the DASH media presentation preparation server 60 encodes media content in a plurality of bitrates to generate an adaptation set and stores it on a disk. The adaptation set include a plurality of media representations. The plurality of media representations may correspond to the plurality of bitrates, respectively. Additionally, the plurality of bitrates may correspond to a plurality of resolutions, respectively. Each media representation includes a plurality of media segments. Moreover, the DASH media presentation preparation server 60 generates media presentation description (MPD) metadata and stores it on a disk. At this point, the MPD metadata includes information on an internet location through which a receiver accesses a plurality of media segments of each of a plurality of media representations.
The MPD delivery function server 70 has an MPD delivery function. The MPD delivery function server 70 transmits MPD metadata to the receiver.
The DASH segment delivery function server 80 has a DASH segment delivery function. The DASH segment delivery function server 80 transmits media segment to the receiver in response to a request of the receiver.
The DASH client device 10 and the DASH segment delivery function server 80 use HTTP. When the DASH client device 10 transmits a media segment to the DASH segment delivery function server 80 through an HTTP request, the DASH segment delivery function server 80 transmits a media segment to the DASH client device 100 through an HPPT response. The media segment may include an MPEG-2 TS media segment and an MP4 media segment.
The DASH client device 10 downloads MPD metadata, measures a current bandwidth, and checks a current bandwidth and an internet location of a media segment in a processable resolution and a processable encoding method, and then transmits an HTTP request for requesting a corresponding media segment to the checked internet location.
FIG. 2 is a block diagram of a typical DASH client.
As shown in FIG. 2, the typical DASH client device 10 includes a DASH access engine 11 and a media engine 12.
The DASH access engine 11 receives and processes MPD metadata and requests necessary media segments from the media segment delivery function server 80 to receive segment data. The DASH access engine 11 takes off metadata describing segments from buffered segment data and obtains timing information and information on other medias and then provides only MPEG media data to the media engine 12.
The media engine 12 corresponds to an MPEG-2 TS Processor (T-STD) and decodes MPEG media data and then plays it.
However, the current MPEG-DASH standard only includes how to deliver media segments and necessary information through HTTP and does not deal with how to transmit/receive an MPD metadata file and a linkage method with broadcasting services. However, the current MPEG-DASH standard defines the MIME Type of MPD metadata as “application/dash+xml” so that a receiver checks the MIME Type of a URL and determines that this URL is the URL of MPD metadata.